Secondary Battery and Method for Manufacturing the Same

ABSTRACT

To solve the above-described objects, a method for manufacturing a secondary battery according to an embodiment of the present invention comprises: manufacturing an electrode assembly in which electrodes and a separator are alternately stacked; inserting the electrode assembly into a battery case through an opening; covering the opening of the battery case; injecting an electrolyte into the battery case through an injection hole formed in the battery case; closing the injection hole; performing a pre-formation process; and applying external force to a switch of a gas discharge device formed on one surface of the battery case, thereby linearly moving a gasket of the gas discharge device and opening a gas discharge hole, such that a first gas generated in the battery case is discharged to an outside of the battery case during the performing of the pre-formation process.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a national phase entry under 35 U.S.C. § 371of International Application No. PCT/KR2018/007928, filed on Jul. 12,2018, published in Korean, which claims priority from Korean PatentApplication No. 10-2017-0089039, filed on Jul. 13, 2017, the disclosuresof which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a secondary battery and a method formanufacturing the same, and more particularly, to a secondary battery inwhich a gas discharge device capable of easily discharging a gas withina battery case is formed to perform pre-formation even after an assemblyprocess and thereby to reduce an assembling time, improve an initialcharging rate, and increase in gas discharge amount, and a method formanufacturing the same.

BACKGROUND ART

Batteries (cells) that generate electric energy through physical orchemical reaction to supply the generated electric energy to the outsideare used when AC power to be supplied to the building is not obtained,or DC power is required according to the living environments surroundedby various electronic devices.

Among such batteries, primary batteries and secondary batteries, whichare chemical cells using chemical reaction, are generally used. Theprimary batteries are consumable cells which are collectively referredto as dry cells. On the other hand, a secondary battery is arechargeable battery that is manufactured by using a material in whichoxidation and reduction processes between current and a material arecapable of being repeated many times. That is, when the reductionreaction to the material is performed by the current, power is charged.When the oxidation reaction to the material is performed by the current,power is discharged. Such charging-discharging are repeatedly performedto generate electricity.

Particularly, a lithium battery using lithium (Li) may be classifiedinto a lithium metal battery, a lithium ion battery, and a lithiumsecondary battery according to types of electrolyte. Here, since thelithium secondary battery has a solid or gel-type electrolyte, even ifthe battery is broken due to an unexpected accident, the electrolytedoes not leak to the outside. Thus, since there is no possibility ofignition or explosion, stability may be secured, and energy efficiencymay be improved.

Such a secondary battery is classified into a pouch type secondarybattery and a can type secondary battery according to a material of acontainer accommodating an electrode assembly. In the pouch typesecondary battery, an electrode assembly is accommodated in a pouch madeof a flexible polymer material having a variable shape. Also, in the cantype secondary battery, an electrode assembly is accommodated in a casemade of a metal or plastic material having a predetermined shape.

The can type secondary battery is classified into a prismatic typesecondary battery in which the case has a polygonal shape and a cylindertype secondary battery in which the case has a cylindrical shapeaccording to the shape of the case.

In the pouch type secondary battery, an injection hole is sealed afteran electrolyte is injected, and then, a formation process is performed.Also, a hole is punched in one surface of the pouch to perform adegassing process for discharging a gas generated in the battery. Here,in the pouch type secondary battery, since the formation process isperformed after the injection hole is completely closed, a charging ratemay be high, and the gas may be quickly discharged. Thus, the secondarybattery may be manufactured within a predetermined process time.

However, in the can type secondary battery, since a hole is not punchedin one surface of the case, and the case is completely sealed after theinjection hole is completely sealed, it is impossible to perform thedegassing process. Thus, in order to prevent moisture from beingpermeated, the pre-formation process is performed in a dry room beforethe injection hole is closed. However, in order to complete themanufacture of the secondary battery within the predetermined processtime, the gas is not completely discharged, and the injection hole isclosed. Thus, only a small amount of gas is discharged, and a portion ofthe gas remains within the case. The completely manufactured secondarybattery may increase in thickness due to the remaining gas. Also, whenthe formation process is performed after the injection hole is closed,there is no method to charge the gas generated in the case.

DISCLOSURE OF THE INVENTION Technical Problem

It is an object to be solved by the present invention to provide asecondary battery in which a gas discharge device capable of easilydischarging a gas within a battery case is provided and a method formanufacturing the same.

The objects of the present invention are not limited to theaforementioned object, but other objects not described herein will beclearly understood by those skilled in the art from descriptions below.

Technical Solution

To achieve the above-described object, a method for manufacturing asecondary battery according to an embodiment of the present inventioncomprises: a step of manufacturing an electrode assembly in whichelectrodes and a separator are alternately stacked; a step of insertingthe electrode assembly into a battery case, which is maintained in apredetermined outer appearance, through an opening; a step of coveringthe opening of the battery case; a step of injecting an electrolyte intothe battery case through an injection hole formed in the battery case; astep of closing the injection hole; a step of performing a pre-formationprocess; and a step of applying external force to a switch of a gasdischarge device formed on one surface of the battery case, therebylinearly moving a gasket of the gas discharge device and opening a gasdischarge hole, such that a first gas generated in the battery case isdischarged to an outside during the step of performing the pre-formationprocess.

Also, after the step of discharging the first gas to the outside of thebattery case, the method may further comprise a step of sealing the gasdischarge device.

Also, the step of sealing of the gas discharge device may furthercomprise: a step of covering the gas discharge device with a cap; and astep of performing laser welding to affix the cap to the battery case.

Also, after the step of discharging the first gas to the outside of thebattery case, the method may further comprise a step of performing aformation process.

Also, after the step of performing of the formation process, the methodmay further comprise: a step of applying the external force to theswitch of the gas discharge device; and a step of linearly moving thegasket of the gas discharge device and opening the gas discharge hole,such that a second gas generated in the battery case is discharged toanoutside of the battery case during the step of performing theformation process.

Also, after the step of discharging the second gas to the outside of thebattery case, the method may further comprise a step of sealing the gasdischarge device.

Also, the step of sealing the gas discharge device may further comprise:a step of covering the gas discharge device with a cap; and a step ofperforming laser welding to affix the cap to the battery case.

Also, the gas discharge device may comprise a restoring part, whichrestores a position of the gasket to close the gas discharge hole whenthe external force is removed.

Also, the restoring of the position of the gasket may be performed byelastic energy stored within the restoring part.

Also, the restoring part may have first and second opposite ends, thefirst end contacting an inner wall of the battery case that faces thegas discharge hole, and the second end contacting the gasket, such thatthe elastic energy is generated by the applying of the external force tothe switch.

Also, when the external force is applied to the switch, the gasket maylinearly move inside of the battery case to compress the restoring part.

Also, the gasket may be integrated with the restoring part.

Also, the gasket may be separated from the restoring part.

Also, the gasket may be integrated with the switch.

To achieve the above-described object, a secondary battery according toan embodiment of the present invention: a battery case accommodating anelectrode assembly therein, in which electrodes and a separator arealternately stacked, and maintained in a predetermined outer appearance;a gasket disposed in the battery case, the gasket being configured topermit selective opening and closing of a gas discharge hole throughwhich an inside and an outside of the battery case communicate with eachother; a switch configured to transmit an external force to the gasketwhen the external force is applied to linearly move the gasket, therebyopening the gas discharge hole; and a restoring part configured torestore a position of the switch when the external force is removed,thereby closing the gas discharge hole.

Also, the restoring part may be configured to store elastic energy, suchthat a position of the gasket is restored when the external force isremoved.

Also, the restoring part may have first and second opposite ends, thefirst end contacting an inner wall of the battery case that faces thegas discharge hole, and the second end contacting the gasket, such thatthe elastic energy is generated when the external force is applied tothe switch.

Also, when the external force is applied to the switch, the gasket maybe configured to linearly move inside of the battery case to compressthe restoring part.

Also, the gasket may be integrated with the restoring part.

Also, the gasket may be separated from the restoring part.

Also, the gasket may be integrated with the switch.

Particularities of other embodiments are included in the detaileddescription and drawings.

Advantageous Effects

The embodiments of the present invention may have at least the followingeffects.

The gas discharge device may be formed in the battery case to performthe pre-formation even after the assembly process and thereby to reducethe assembling time, improve the initial charging rate, and increase ingas discharge amount.

Also, in the manufacturing process of the secondary battery, the gasremaining in the battery case may be easily discharged by only pushingthe switch of the gas discharge device.

Also, the pressure within the battery case may be lowered than theatmospheric pressure after the electrolyte is injected to completelydischarge the gas remaining in the battery case.

The effects of the prevent invention are not limited by theaforementioned description, and thus, more varied effects are involvedin this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for manufacturing a can typesecondary battery according to a related art.

FIG. 2 is a flowchart illustrating a method for manufacturing asecondary battery according to an embodiment of the present invention.

FIG. 3 is an exploded perspective view illustrating the secondarybattery according to an embodiment of the present invention.

FIG. 4 is an enlarged lateral cross-sectional view taken along line A-A′of FIG. 3 in the secondary battery according to an embodiment of thepresent invention.

FIG. 5 is an enlarged lateral cross-sectional view taken along line A-A′of FIG. 3 in the secondary battery according to another embodiment ofthe present invention.

FIG. 6 is a perspective view illustrating a state in which a gasdischarge device is sealed according to an embodiment of the presentinvention.

MODE FOR CARRYING OUT THE INVENTION

Advantages and features of the present disclosure, and implementationmethods thereof will be clarified through following embodimentsdescribed with reference to the accompanying drawings. The presentinvention may, however be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Further, the present invention is only definedby scopes of claims. Like reference numerals refer to like elementsthroughout.

Unless terms used in the present invention are defined differently, allterms (including technical and scientific terms) used herein have thesame meaning as generally understood by those skilled in the art. Also,unless defined clearly and apparently in the description, the terms asdefined in a commonly used dictionary are not ideally or excessivelyconstrued as having formal meaning.

In the following description, the technical terms are used only forexplaining a specific exemplary embodiment while not limiting theinventive concept. In this specification, the terms of a singular formmay comprise plural forms unless specifically mentioned. The meaning of‘comprises” and/or “comprising’ does not exclude other componentsbesides a mentioned component.

Hereinafter, preferred embodiments will be described in detail withreference to the accompanying drawings.

FIG. 1 is a flowchart illustrating a method for manufacturing a can typesecondary battery according to a related art.

As described above, in the pouch type secondary battery, since a hole ispunched in one surface of a pouch, a pre-formation or formation processmay be performed after an assembly process to discharge a gas to theoutside. However, in the can type secondary battery, since a hole is notpunched in one surface of a case, it is impossible to discharge a gasgenerated in the case when a formation process is performed after aninjection hole for an electrolyte is closed.

In more detail, a process of manufacturing the secondary battery islargely classified into three processes such as an electrode plateprocess, an assembly process, and a formation process. The electrodeplate process is a process of manufacturing a positive electrode plateand a negative electrode plate. Here, an active material may be appliedto a base material to manufacture the positive electrode plate and thenegative electrode plate.

The assembly process (S101 to S108) is a process of assembling thesecondary battery. Hereinafter, the assembly process will be describedwith reference to a flowchart of FIG. 1. First, the manufacturedpositive and negative electrode plates and a separator may bealternately stacked to manufacture an electrode assembly (S101). Also,the electrode assembly is inserted into a battery case through anopening of the battery case (S102), and the opening of the battery caseis covered (S103). Here, in the can type secondary battery, the batterycase is maintained to have a predetermined outer appearance. Thus, whenthe opening of the battery case is covered, a top cap assembly is used.Also, the top cap assembly is welded to an outer wall of the batterycase to cover the opening of the battery case.

After the battery case is covered, an electrolyte is primarily injectedthrough an injection hole formed in the battery case (S104). Since theelectrolyte is secondarily injected later, only a small amount ofelectrolyte is injected when the electrolyte is primarily injected.Then, a pre-formation process is performed (S105). The pre-formationprocess is a process of forming an SEI layer on a surface of theelectrode plates of the electrode assembly to generate charges. Forthis, initial charging is performed on the electrode assembly. Here, agas is generated in the battery case. According to the related art, thepre-formation process is included in the assembly process. Thus, whenthe secondary battery is still in an assembly line, the pre-formationprocess is performed in a dray room without closing the injection hole.However, since it is difficult to perform the pre-formation process fora long time in the state in which the injection hole is opened, only asmall amount of gas is discharged (S106), and thus, the rest gas isremained in the battery case. If the remaining gas is too much, thesecondary battery may increase in thickness. Also, while the gas isdischarged to the outside through the injection hole, the electrolytemay be discharged to the outside due to overflow. However, since theassembly time is determined in the assembly process, it does not takemuch time to discharge the gas. Thus, in order to reduce an amount ofremaining gas without excessively consuming the assembly time, thecharging rate does not increase at the initial charging, and also, thegas has to be charged at a charging rate of 10% to 13%. Also, the nextprocess is performed in the state in which only a small amount of gas isdischarged.

Then, the electrolyte is secondarily injected (S107). Of course, whenthe electrolyte is secondarily injected, a pressure is lowered so thatthe vicinity thereof is close to a vacuum state, or the secondarybattery is pressed. In this process, the gas remaining in the batterycase may be further discharged. However, in this process, the gas withinthe battery case is not completely discharged, and also, an amount ofgas remaining in the battery case is not accurately measured. Theinjection hole is closed as the last step of the assembly process(S108). Thus, the assembly of the secondary battery is completed.However, since the injection hole is closed in the state in which thegas is capable of remaining in the battery case, the secondary batterymay increase still in thickness.

Lastly, a formation process is performed (S109). The formation processis a process of finalizing the charging so that the secondary battery iscapable of supplying electric power. Here, an external power source maybe connected to the electrodes of the secondary battery to perform thecharging, and then, an aging process may be further performed. When thecharging is performed in the formation process, the charging may beperformed at the maximum charging rate unlike the initial charging. Theaging process is a process of storing the assembled secondary batteryfor a predetermined time at specific temperature and humidity. Here, theelectrolyte is sufficiently dispersed in the secondary battery tooptimize movement of ions.

Since the formation process is a process different from the assemblyprocess, the formation process may be performed after getting out of theassembly line. However, while the formation process is performed, a gasmay be generated again in the battery case. However, since the injectionhole of the secondary battery is already closed, the generated gas maynot be discharged, and thus, the secondary battery may increase inthickness.

FIG. 2 is a flowchart illustrating a method for manufacturing asecondary battery (see reference numeral 1 of FIG. 3) according to anembodiment of the present invention.

In the secondary battery 1 according to an embodiment of the presentinvention comprises a gas discharge device (see reference numeral 12 ofFIG. 3). Thus, a pre-formation process may not be performed in anassembly process but may performed after getting out of an assemblyline. Also, even after the formation process is performed, a gas withina battery case (see reference numeral 11 of FIG. 3) may be discharged tothe outside. Hereinafter, the method for manufacturing the secondarybattery 1 according to an embodiment of the present invention will bedescribed with reference to the flowchart illustrated in FIG. 2.

First, an active material is applied to a base material through anelectrode plate process to manufacture a positive electrode plate and anegative electrode plate. Also, in an assembly process (S201 to S205),first, the manufactured positive and negative electrode plates and aseparator are alternately stacked to manufacture an electrode assembly(see reference numeral 13 of FIG. 3) (S201). The electrode assembly 13is inserted into the battery case 11 through an opening of the batterycase 11 (S202). Then, an opening-side outer wall of the battery case 11is welded to a rear case (see reference numeral 111 of FIG. 3) to coverthe opening of the battery case 11 (S203).

After the battery case 11 is covered, an electrolyte is injected throughan injection hole formed in the battery case 11 (S204). Here, unlike themethod according to the related art, the electrolyte is injected onlyonce without dividing into primary and secondary injections. Thus, asmall amount of electrolyte is not injected, but a fixed amount ofelectrolyte is injected. Also, the injection hole is closed as the laststep of the assembly process (S205). Thus, the assembly of the secondarybattery 1 is completed.

When the assembly of the secondary battery 1 is completed, the electrodeassembly gets out of the assembly line. Then, a pre-formation process isperformed (S206). Here, in the secondary battery 1 according to anembodiment of the present invention, the gas discharge device 12 isformed in the battery case 11. Thus, the pre-formation process may beperformed to improve an initial charging rate to a very high level ofapproximately 60% to 70%. Also, although an amount of first gasgenerated while the pre-formation process is performed is much, theassembly process is already completed, the first gas may be sufficientlydischarged without being limited to an assembly time (S207). Thus, thegas remaining in the battery case 11 may be maximally reduced to preventthe secondary battery 1 from increasing in thickness.

Furthermore, since a manipulation method of the gas discharge device 12is very simple, the first gas remaining in the battery case 11 may beeasily discharged by only pushing a switch (see reference numeral 121 ofFIG. 3) of the gas discharge device 12.

After the pre-formation process is performed, a formation process isperformed (S208). When the formation process is performed, a second gasis generated in the battery case 11. However, like the first gas, thesecond gas may be easily discharged by only pushing the switch 121 ofthe gas discharge device 12.

Here, the pre-formation process may be performed, and then, theformation process may be immediately performed without discharging thefirst gas. That is, the step S207 may be omitted, and the step S208 maybe performed immediately. However, since an amount of first gasgenerated in the pre-formation process is too much, it is preferablethat the step S208 is performed after the step S207 is performed.

Also, a separate pressure pump may be connected to the gas dischargedevice 12. In this case, a pressure within the battery case 11 may belowered than the atmospheric pressure. Thus, even though a small amountof gas remains in the battery case 11, the gas may be completelydischarged to the outside.

FIG. 3 is an exploded perspective view illustrating the secondarybattery 1 according to an embodiment of the present invention.

Hereinafter, the method for manufacturing the secondary battery 1according to an embodiment of the present invention has been described.As described above, since the gas discharge device 12 is formed in thesecondary battery 1 according to an embodiment of the present invention,the above-described method may be performed. Hereinafter, the gasdischarge device 12 formed in the secondary battery according to anembodiment of the present invention will be described.

As illustrated in FIG. 3, since the secondary battery 1 according to anembodiment of the present invention is the can type secondary battery,the electrode assembly 13 is accommodated in the battery case 11 made ofa metal or plastic having a predetermined shape. Although a prismatictype battery having a polyhedron or polygonal column shape isillustrated in FIG. 3, the embodiment of the present invention is notlimited thereto. For example, the battery case 11 may be a cylinder typebattery having a cylindrical shape. That is, if the battery case 11 isprovided in the can type having a predetermined shape, various kinds ofsecondary batteries 1 may be provided without limitation.

As illustrated in FIG. 3, the gas discharge device 12 is formed at oneside of the secondary battery 1. In the general gas discharge device 12,when the gas is generated from the electrolyte while the secondarybattery 1 is used, the internal pressure increases. Then, when theinternal pressure is above a predetermined pressure, the gas dischargedevice 12 is automatically opened to discharge the gas to the outside.That is, when the pressure within the battery case 11 is less than thepredetermined pressure, the gas discharge device 12 is not opened. Onthe other hand, the gas discharge device 12 according to an embodimentof the present invention may discharge the gas to the outside eventhough the pressure within the battery case 11 is not above thepredetermined pressure. Even if a separate vacuum pump is used, the gasmay be easily discharged to the outside even though the pressure withinthe battery case 11 is not above the atmospheric pressure.

Since all of the electrolyte and the gas may be accommodated in thebattery case 11, and the gas has density that is very lower than that ofthe electrolyte, the electrolyte is disposed in a lower portion of thebattery case 11, and the gas is disposed in an upper portion of thebattery case 11. Thus, in order to select only the gas and then easilydischarge the gas, is preferable that the gas discharge device 12 isdisposed above the battery case 11.

FIG. 4 is an enlarged lateral cross-sectional view taken along line A-A′of FIG. 3 in the secondary battery 1 according to an embodiment of thepresent invention.

A gas discharge hole for allowing the inside and outside of the batterycase 11 to communicate with each other is formed in one side of thebattery case 11, and the gas discharge device 12 opens and closes thegas discharge hole. As illustrated in FIG. 4, the gas discharge device12 according to an embodiment of the present invention comprises aswitch 121, a gasket 122, a restoring part 123.

The switch 121 is formed to be exposed to the outside of the batterycase 11. It is preferable that the switch 121 is formed to protrude froma discharge hole. Also, a user may easily apply external force from theoutside the secondary battery 1 by using a finger or the like. When theuser applies the external force to the switch 121, the switch 121transmits the external force to the gasket 122 to allow the gasket 122to linearly move.

The gasket 122 is formed in the battery case 11 to open and close thegas discharge hole. The gas generated in the battery case 11 may bedischarged to the outside through the gas discharge hole. Here, thegasket 122 is formed in the battery case 11 to receive restoring forceapplied from the inside to the outside of the battery case 11 throughthe restoring part 123. Thus, the gasket 122 may seal the gas dischargehole. However, when the external force is applied to the switch 121, thegasket 122 receives the external force from the switch 121 to linearlymove. Here, the gasket 122 receives the external force from the outsideto the inside of the battery case 11. Thus, the gasket 122 linearlymoves from the inside to the outside of the battery case 11 in adirection in which the external force is applied. Thus, the gasket 122opens the gas discharge hole to discharge the gas within the batterycase 11 to the outside.

The restoring part 123 provides restoring force to the gasket so thatthe gasket 122 seals the gas discharge hole. It is preferable that therestoring part 123 is made of a material having elasticity.Particularly, according to an embodiment of the present invention, therestoring part 123 may be made of a metal material having elasticitysuch as a spring and may have a shape that lengthily extends in an axialdirection while forming a circle having a predetermined size, forexample, a spiral shape. However, the embodiment of the presentinvention is not limited thereto. For example, the restoring part 123may have various sizes and shape as long as the restoring part 123generates the restoring force to provide the generated restoring forceto the gasket 122.

The restoring force may be an actual elastic force generated from therestoring part 123. That is, when the external force is applied throughthe switch 121, the restoring part 123 is deformed in a longitudinaldirection while the gasket 122 linearly moves. Here, elastic force isgenerated in proportion to a degree of deformation and a modulus ofelasticity. Here, the restoring part 123 has to be deformed in thelongitudinal direction by the external force. Thus, as illustrated inFIG. 4, it is preferable that both ends of the restoring part 123respectively contact an inner wall of the battery case 11, which facesthe gas discharge hole, and one surface of the gasket 122. Thus, thedirection in which the external force is applied and the direction inwhich the restoring part 123 is deformed may match each other togenerate the largest elastic force.

However, the embodiment of the present invention is not limited thereto.For example, in order to restore the gasket 122 to its originalposition, the restoring force may be provided in a different manner. Forexample, a magnet may be attached to each of the inner wall of thebattery case 11 and one surface of the gasket 122 to generate magneticforce or generate electric force by generating electricity. That is, therestoring force may be provided in various manners without limitation aslong as the gasket 122 is restored in its original position when theexternal force is removed.

FIG. 5 is an enlarged lateral cross-sectional view taken along line A-A′of FIG. 3 in the secondary battery 1 according to another embodiment ofthe present invention.

As illustrated in FIG. 5, a gas discharge device 12 a according toanother embodiment of the present invention comprises a switch 121 a, agasket 122 a, and a restoring part 123 a. Hereinafter, descriptionsduplicated with those of the gas discharge device 12 according to theforegoing embodiment of the present invention will be omitted.

According to another embodiment of the present invention, the restoringpart 123 a may have elasticity. However, the restoring part 123 a maynot have a spring shape but have a simple column shape as illustrated inFIG. 5. Here, it is preferable that the restoring part 123 a is made ofa non-metallic material such as rubber or polyurethane and also made ofa material having elasticity.

According to various embodiments of the present invention, the switch12, the gasket 122, and the restoring part 123 of the gas dischargedevice 12 may be formed to be separated from each other. Alternatively,at least two components may be integrated with each other. Particularly,the switch 121 and the gasket 122 may be manufactured to be separatedfrom each other or integrated with each other. Also, the gasket 122 andthe restoring part 123 may be manufactured to be separated from eachother or integrated with each other. Furthermore, the switch 121, thegasket 122, and the restoring part 123 may be manufactured to beintegrated with each other. Here, when the restoring part 123 is made ofa material such as rubber, each of the switch 121 and the gasket 122 maybe made of the same material.

It is preferable that the external force applied to the switch 121 is apressure. Here, when the user pushes the switch 121 by using a finger,the switch 121 transmits the external force to the gasket 122 so thatthe gasket 122 linearly moves. Also, if one end of the restoring part123 contacts the inner wall of the battery case 11, which faces the gasdischarge hole, the gasket 122 linearly moves, and thus, the restoringpart 123 is compressed to generate elasticity. However, if one end ofthe restoring part 123 contacts the inner wall of the battery case 11,in which the gas discharge hole is formed, the gasket 122 linearlymoves, and thus, the restoring part 123 is tensioned to generateelasticity.

The external force may be tensile force without being limited to thepressure. Here, the gasket 122 is not formed in the battery case 11 butformed outside the battery case so that the restoring part 123 receivesthe restoring force from the outside to the inside. Thus, the gasket 122may close the gas discharge hole. However, when the external force isapplied to the switch 121, i.e., the user pulls the switch 121, thegasket 122 receives the external force from the switch 121 to linearlymove. Here, the gasket 122 receives the external force from the insideto the outside of the battery case 11. Thus, the gasket 122 linearlymoves from the outside to the inside of the battery case 11 in adirection in which the external force is applied. Thus, the gasket 122opens the gas discharge hole to discharge the gas within the batterycase 11 to the outside.

That is, the secondary battery 1 according to various embodiments of thepresent invention may have various structures as long as the gasket 122moves to open the gas discharge hole when the external force is appliedto the switch 121, and the gasket 122 is restored by the restoring forceof the restoring part 123 to close the gas discharge hole when theexternal force is removed.

FIG. 6 is a perspective view illustrating a state in which the gasdischarge device 12 is sealed according to an embodiment of the presentinvention.

In the gas discharge device 12 according to an embodiment of the presentinvention, the gas generated in the battery case 11 is discharged to theoutside. Thus, the gas discharge device 12 may be used in variousprocesses of manufacturing the secondary battery 1, the pre-formationprocess, and the formation process. However, when the manufacture of thesecondary battery 1 is completed, and the secondary battery is sold togeneral consumers, ordinary users other than experts may inadvertentlyoperate the gas discharge device 12 while using the secondary battery 1.Here, the electrolyte may leak through the gas discharge hole, and whenthe pressure within the battery case 11 is less than the atmosphericpressure, external air may be introduced into the battery case 11. Thus,as illustrated in FIG. 6, the gas discharge device 12 is covered by acap 14 and then sealed.

If a gas is generated in the battery case 11 while the secondary battery1 is used, the secondary battery 1 may increase in thickness. Here, whenthe sealed cap 14 is removed, and external force is applied to theswitch 121 of the gas discharge device 12, the gas within the batterycase 11 may be discharged to the outside.

If the cap 14 has a very small size, the cap 14 may not fully cover theswitch 121 of the gas discharge device 12, and thus, the switch 121 maybe exposed to the outside. On the other hand, if the cap 14 has a verylarge size, the gas discharge device 12 may not be easily sealed, andalso, the overall outer appearance of the secondary battery 1 may bedeformed. Thus, it is preferable that the cap has a size that is enoughto fully cover the switch 121 of the gas discharge device 12 and easilyseal the gas discharge device 12. More preferably, if each of the cap 14and the switch 121 of the gas discharge device 12 has a circular shape,the cap 14 may have a diameter greater 1.2 times to 1.5 times than thatof the gas discharge device 12.

Preferably, the sealing of the gas discharge device 12 by using the cap12 may be performed after the formation process is completed, and thesecond gas is discharged to the outside. However, the embodiment of thepresent invention is not limited thereto. For example, the sealing ofthe gas discharge device 12 may be performed after the pre-formationprocess is completed, and only the first gas is discharged to theoutside. That is, the gas discharge device 12 may be sealed before theformation process. This is done because an amount of second gasgenerated through the formation process is generally greater than thatof second gas generated through the pre-formation process. If it is, theamount of generated second gas is expected to be very small, the gasdischarge device 12 may be sealed before the formation process so at toreduce the manufacturing time of the secondary battery 1.

After the gas discharge device 12 is covered by the cap 14, the cap 14may be fixed to the battery case 11 through laser welding or the like.However, the embodiment of the present invention is not limited thereto.For example, the cap 14 may be fixed to the battery case 11 throughvarious manners such as electric welding, gas welding, and the like aslong as the cap 14 is fixed to the battery case 11.

Those with ordinary skill in the technical field of the presentinvention pertains will be understood that the present invention can becarried out in other specific forms without changing the technical ideaor essential features. Therefore, the above-disclosed embodiments are tobe considered illustrative and not restrictive. Accordingly, the scopeof the present invention is defined by the appended claims rather thanthe foregoing description and the exemplary embodiments describedtherein. Various modifications made within the meaning of an equivalentof the claims of the invention and within the claims are to be regardedto be in the scope of the present invention.

1. A method for manufacturing a secondary battery, the methodcomprising: manufacturing an electrode assembly in which electrodes anda separator are alternately stacked; inserting the electrode assemblyinto a battery case through an opening; covering the opening of thebattery case; injecting an electrolyte into the battery case through aninjection hole formed in the battery case; closing the injection hole;performing a pre-formation process; and applying external force to aswitch of a gas discharge device formed on one surface of the batterycase, thereby linearly moving a gasket of the gas discharge device andopening a gas discharge hole, such that a first gas generated in thebattery case is discharged to an outside of the battery case during theperforming of the pre-formation process.
 2. The method of claim 1,further comprising, after the first gas is discharged to the outside ofthe battery case, sealing the gas discharge device.
 3. The method ofclaim 2, wherein the sealing of the gas discharge device furthercomprises: covering the gas discharge device with a cap; and performinglaser welding to affix the cap to the battery case.
 4. The method ofclaim 1, further comprising, after the first gas is discharged to theoutside of the battery case, performing a formation process.
 5. Themethod of claim 4, further comprising, after the performing of theformation process: applying the external force to the switch of the gasdischarge device; and linearly moving the gasket of the gas dischargedevice and opening the gas discharge hole, such that a second gasgenerated in the battery case is discharged to an outside of the batterycase during the performing of the formation process.
 6. The method ofclaim 5, further comprising, after the second gas is discharged to theoutside of the battery case, sealing the gas discharge device.
 7. Themethod of claim 6, wherein the step of sealing the gas discharge devicefurther comprises: covering the gas discharge device with a cap; andperforming laser welding to affix the cap to the battery case.
 8. Themethod of claim 1, wherein the gas discharge device comprises arestoring part, the method further comprising restoring a position ofthe gasket and closing the gas discharge hole when the external force isremoved.
 9. The method of claim 8, wherein the restoring of the positionof the gasket is performed by elastic energy stored within the restoringpart.
 10. The method of claim 9, wherein the restoring part has firstand second opposite ends, the first end contacting an inner wall of thebattery case, that faces the gas discharge hole, and the second endcontacting the gasket, such that the elastic energy is generated by theapplying of the external force to the switch.
 11. The method of claim 9,wherein, when the external force is applied to the switch, the gasketlinearly moves inside of the battery case to compress the restoringpart.
 12. A secondary battery comprising: a battery case accommodatingan electrode assembly therein, in which electrodes and a separator arealternately stacked; a gasket disposed in the battery case, the gasketbeing configured to permit selective opening and closing of a gasdischarge hole through which an inside and an outside of the batterycase communicate with each other; a switch configured to transmit anexternal force to the gasket when the external force is applied tolinearly move the gasket, thereby opening the gas discharge hole; and arestoring part configured to restore a position of the switch when theexternal force is removed, thereby closing the gas discharge hole. 13.The secondary battery of claim 12, wherein the restoring part isconfigured to store elastic energy, such that a position of the gasketis restored when the external force is removed.
 14. The secondarybattery of claim 13, wherein the restoring part has first and secondopposite ends, the first end contacting an inner wall of the batterycase that faces the gas discharge hole, and the second end contactingthe gasket, such that the elastic energy is generated when the externalforce is applied to the switch.
 15. The secondary battery of claim 13,wherein the gasket is configured to linearly move inside of the batterycase to compress the restoring part when the external force is appliedto the switch.